1. Field of the Invention
The present invention is related to a liquid crystal compound, and in particular to a liquid crystal compound having a low nematic phase floor temperature and high optical anisotropy.
2. Description of Related Art
In order to enhance characteristics of a liquid crystal display device, a liquid crystal composition used by the device must have suitable properties. The liquid crystal composition usually includes a plurality of liquid crystal compounds, and each of the liquid crystal compounds has one or a plurality of the following properties: stable chemical and physical properties; having a high clearing point (a liquid crystal phase—isotropic phase transformation temperature); a low liquid crystal phase (nematic phase, smectic phase, etc.) floor temperature, especially a low nematic phase floor temperature; low viscosity; having suitable optical anisotropy; having suitable dielectric constant anisotropy; and superb compatibility with other liquid crystal compounds.
By using the composition which includes the liquid crystal compound with stable chemical and physical properties in the display device, the voltage holding ratio of the liquid crystal composition is enhanced.
By using the composition which includes the liquid crystal compound with a high clearing point and a low liquid crystal phase floor temperature, the nematic phase temperature range of the liquid crystal composition is expanded, so that the display device is able to be used in a wide temperature range.
Moreover, by using the composition which includes the compound with low viscosity in the display device, the response speed of the liquid crystal composition is increased; by using the composition which includes the compound with suitable optical anisotropy in the display device, the contrast of the display device is increased.
When developing a liquid crystal material of optical anisotropy, birefringence is able to be increased by increasing conjugated structures on the long molecular axis. Generally, a structure with at least three benzene rings is required for Δn to have a chance to be greater than 0.2. However, a liquid crystal compound which includes the structure with at least three benzene rings makes the nematic phase floor temperature increase, thereby reducing the temperature range in which the liquid crystal compound may be used.